Brittle or Quasi-Brittle Fracture of Engineering Materials 2016

1Department of Engineering Design and Materials, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway 2Faculty of Mechanical Engineering, Politehnica University of Timisoara, Blvd. M. Viteazu, Nr. 1, 300222 Timisoara, Romania 3Fatigue and Fracture Research Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics, School of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran 16846, Iran 4Institute of Strength Physics and Material Science, Department of Mechanical Engineering & Aeronautics, Russian Academy of Sciences, Siberian Branch, Tomsk 634021, Russia 5Laboratory of Technology & Strength of Materials (LTSM), Department of Mechanical Engineering & Aeronautics, University of Patras, 26500 Patras, Greec

Global, regional, and national burden of disorders affecting the nervous system, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BackgroundDisorders affecting the nervous system are diverse and include neurodevelopmental disorders, late-life neurodegeneration, and newly emergent conditions, such as cognitive impairment following COVID-19. Previous publications from the Global Burden of Disease, Injuries, and Risk Factor Study estimated the burden of 15 neurological conditions in 2015 and 2016, but these analyses did not include neurodevelopmental disorders, as defined by the International Classification of Diseases (ICD)-11, or a subset of cases of congenital, neonatal, and infectious conditions that cause neurological damage. Here, we estimate nervous system health loss caused by 37 unique conditions and their associated risk factors globally, regionally, and nationally from 1990 to 2021.MethodsWe estimated mortality, prevalence, years lived with disability (YLDs), years of life lost (YLLs), and disability-adjusted life-years (DALYs), with corresponding 95% uncertainty intervals (UIs), by age and sex in 204 countries and territories, from 1990 to 2021. We included morbidity and deaths due to neurological conditions, for which health loss is directly due to damage to the CNS or peripheral nervous system. We also isolated neurological health loss from conditions for which nervous system morbidity is a consequence, but not the primary feature, including a subset of congenital conditions (ie, chromosomal anomalies and congenital birth defects), neonatal conditions (ie, jaundice, preterm birth, and sepsis), infectious diseases (ie, COVID-19, cystic echinococcosis, malaria, syphilis, and Zika virus disease), and diabetic neuropathy. By conducting a sequela-level analysis of the health outcomes for these conditions, only cases where nervous system damage occurred were included, and YLDs were recalculated to isolate the non-fatal burden directly attributable to nervous system health loss. A comorbidity correction was used to calculate total prevalence of all conditions that affect the nervous system combined.FindingsGlobally, the 37 conditions affecting the nervous system were collectively ranked as the leading group cause of DALYs in 2021 (443 million, 95% UI 378–521), affecting 3·40 billion (3·20–3·62) individuals (43·1%, 40·5–45·9 of the global population); global DALY counts attributed to these conditions increased by 18·2% (8·7–26·7) between 1990 and 2021. Age-standardised rates of deaths per 100 000 people attributed to these conditions decreased from 1990 to 2021 by 33·6% (27·6–38·8), and age-standardised rates of DALYs attributed to these conditions decreased by 27·0% (21·5–32·4). Age-standardised prevalence was almost stable, with a change of 1·5% (0·7–2·4). The ten conditions with the highest age-standardised DALYs in 2021 were stroke, neonatal encephalopathy, migraine, Alzheimer's disease and other dementias, diabetic neuropathy, meningitis, epilepsy, neurological complications due to preterm birth, autism spectrum disorder, and nervous system cancer.InterpretationAs the leading cause of overall disease burden in the world, with increasing global DALY counts, effective prevention, treatment, and rehabilitation strategies for disorders affecting the nervous system are needed

Recent Developments in Brittle and Quasi-Brittle Failure Assessment of Graphite by Means of SED

Brittle fracture of polycrystalline graphite under tension, in-plane shear and torsion loading is studied experimentally and theoretically using prismatic and axisymmetric specimens weakened by sharp and rounded-tip V-notches. The main purpose is twofold. First, to provide a new set of experimental data from notched samples made of isostatic polycrystalline graphite with different values of notch opening angles and root radii, which should be useful to engineers engaged with static strength analysis of graphite components. At the best of authors' knowledge, data from notch specimens are very scarce in the literature for this material. Second, to apply a fracture criterion based on the strain energy density (SED) averaged over a well-defined control volume surrounding the notch tip, extending what was made by the present authors for in-plane tension-shear loading conditions in notched specimens made of other materials. Good agreement is found between the experimental data related to the critical loads to failure and the theoretical assessments based on the constancy of the mean SED over the material-dependent control volume. \ua9 (2014) Trans Tech Publications

Crack tip asymptotic field and K-dominant region for anisotropic semi-circular bend specimen

This study reports the coefficients of the crack tip asymptotic field for the semi-circular bend (SCB) specimen made of anisotropic rocks when subjected to pure mode loading. The finite element over-deterministic method is employed to determine the singular and higher order terms of the crack tip asymptotic field for a wide range of geometry and anisotropy parameters associated with the Mode I SCB test. These parameters are helpful when analysing the fracture path and failure mechanism of anisotropic rocks in cases where the process zone is large compared to the crack length. We also apply an energy-based criterion on the crack tip fields to evaluate the size of the K-dominant region as a function of geometry configuration and anisotropy. It is concluded that the ISRM-suggested size requirement for the SCB samples of rock can yield underestimated values of fracture toughness due to the constraints applied to the FPZ development

Effect of Dental Restorative Material Type and Shade on Characteristics of Two-Layer Dental Composite Systems

Abstract The purpose of this study was to investigate the effects of shade and material type and shape in dental polymer composites on the hardness and shrinkage stress of bulk and two-layered restoration systems. For this purpose, some bulk and layered specimens from three different shades of dental materials were prepared and light-cured. The experiments were carried out on three types of materials: conventional restorative composite, nanohybrid composite and nanocomposite. Micro-indentation experiment was performed on the bulk and also on each layer of layered restoration specimens using a Vicker's indenter. The interface between the two layers was studied by scanning electron microscopy (SEM). The results revealed significant differences between the values of hardness for different shades in the conventional composite and also in the nanohybrid composite. However, no statistically significant difference was observed between the hardness values for different shades in the nanocomposite samples. The layered restoration specimens of different restorative materials exhibited lower hardness values with respect to their bulk specimens. The reduction in the hardness value of the layered conventional composite samples was higher than those of the nanocomposite and nanohybrid composite specimens indicating more shrinkage stresses generated in the conventional composite restorations. According to the SEM images, a gap was observed between the two layers in the layered restorations

Theory and experiment on true mode II fracturing of rocks

This paper discusses the use of the double-edge notched Brazilian disk test (DNBD) for measuring true mode II fracture toughness of rocks. The term true emphasises that in this test, not only is the crack tip loading shear-based, but also the material failure is shear-induced. Conventional mode II tests typically experience dominantly tensile failure. We introduce a fracture growth criterion that explains where and how a shear-based fracture extension occurs. Our theoretical analysis demonstrates that large values of compressive T-stress in the DNBD specimen significantly help inducing a true mode II fracturing. Crack tip parameters are computed by finite element analyses for various notch lengths and loading angles. These values are then employed to determine the geometry and loading condition for the optimal performance of the test. We also compare the DNBD with two other available tests for measuring true mode II fracture toughness, and show that the DNBD test typically has a lower contribution of mode I loading than the two alternative approaches and, therefore, better approximates the true mode II condition while at the same time being the experimentally simplest. Three types of rocks (limestone, marble and granite) were tested using the new approach and their true mode II fracture toughness is reported for two different crack lengths. The measured true mode II fracture toughness is compared with the mode I fracture toughness obtained from the semi-circular bending test. © 2020 The Author(s)ISSN:0013-7944ISSN:1873-731

A New Criterion for Rupture Assessment of Rubber-Like Materials under Mode-I Crack Loading: The Effective Stretch Criterion

A new criterion is presented for fracture assessment of rubber-like materials weakened by a mode I crack. The criterion is based on two main assumptions: the existence of a damage zone around the crack tip and the dominant uniaxial nature of the stress field near the crack in rubber-like materials. Considering these key features and employing the concepts of well-known eight-chain model, first, a failure criterion called the "Effective Stretch Criterion" has been proposed. Then, a procedure has been elaborated to calibrate the material parameters in the criterion. The criterion, finally, has been validated by using two sets of experimental data available in the literature

3D fracture behaviour of graphite specimens weakened by V- notches with end holes under mixed mode (I+II) loading

In the present contribution, the static strength of isostatic graphite using V-notched specimens with end holes under mixed mode loading is investigated considering 3D simulation. An experimental program was performed and in total, 14 new experimental data are provided in the paper for the first time. The criterion based on the averaged value of the strain energy density over a control volume which has been applied to assess the static strength of the different 2D specimens, is developed in the current work by modification of the control volume to assess the thickness effect on the static strength of graphite specimens. A sound agreement is found between the experimental data and the results obtained from the strain energy density criterion.Peer Reviewe